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Grilli F.,Karlsruhe Institute of Technology | Chervyakov A.,Institute for Advanced Sustainability Studies | Zermeno V.,Karlsruhe Institute of Technology | Marian A.,Institute for Advanced Sustainability Studies | And 3 more authors.
Physica C: Superconductivity and its Applications | Year: 2014

Cables made of MgB2 superconductors are currently explored as a viable solution for transporting high electrical power in the AC regime. In order to be competitive against the DC solution, the cables need to have an acceptable level of AC losses. In this contribution, we discuss the main aspects relevant for designing a cable with a sufficiently low AC loss level. To this end, we perform finite-element-method (FEM) simulations to determine the current and field distributions and calculate the AC losses of such cable configuration. For current capacities of 2-5 kA (peak), power cables are assembled from a relatively small number of MgB2 strands. The performance of such cables strongly depends on the current and field distributions, which are in turn influenced by the number and the arrangement of the superconducting components and also by the magnetic properties of supporting materials. Numerical simulations can help to test different cable configurations and provide important insights for optimizing the cable's design. The numerical model includes the field dependence of the superconductor's critical current density Jc(B) as well as the non-linear properties of magnetic materials. © 2014 Published by Elsevier B.V.

Musenich R.,National Institute of Nuclear Physics, Italy | Nardelli D.,Columbus Superconductors | Brisigotti S.,Columbus Superconductors | Pietranera D.,Columbus Superconductors | And 5 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2016

Among the characteristics required by a spaceborne superconducting magnet, lightness and reliability are the most important. The use of titanium clad magnesium diboride conductors fulfills both the requirements: it allows avoiding helium cryogenics, it guarantees good stability, and it has density below 4500 kg/m 3. A conductor based on a Ti-MgB 2 tape was developed in the framework of a study on superconducting shields to protect astronauts against cosmic rays, co-funded by the European Union (EU FP7 SR2S Project). The magnet is designed to operate at 10 K and below 4 T at the conductor. The prototype tape, manufactured via ex situ method, is 3 mm wide and 0.5 mm thick and has 19 MgB 2 filaments. According to the original design, a pure aluminum strip should be coupled to the tape in order to protect the conductor in case of quench. However, due to technical problems, the process was completed by soldering a copper strip on titanium. The conductor and its manufacture process are described in this paper. © 2015 IEEE.

Vignolo M.,CNR Institute of Neuroscience | Bovone G.,University of Genoa | Matera D.,CNR Institute of Neuroscience | Nardelli D.,Columbus Superconductors | And 3 more authors.
Chemical Engineering Journal | Year: 2014

In the present paper a new process for large scale production of nano-sized boron is reported. The process can be summarized in several steps: boron oxide solubilization in hot water, cryogenic freezing of liquid phase, freezing-drying process, magnesiothermic reduction of boron oxide, boron purification. Each step is described in order to show the innovations and then the purified boron has been employed to synthesize the superconducting MgB2 powder. It is worth to note that for the first time the same MgB2 precursors were used to prepare the superconducting phase following four different techniques and the results directly compared. So several MgB2 conductors were prepared applying different techniques, ex-situ, in-situ, via MgB4 and RLI, and then their superconducting properties investigated. Furthermore morphology, grain size and purity of B and MgB2 powder were analyzed by SEM analysis and X-ray diffraction technique. © 2014 Elsevier B.V.

Pitel J.,Slovak Academy of Sciences | Melisek T.,Slovak Academy of Sciences | Tropeano M.,Columbus Superconductors | Nardelli D.,Columbus Superconductors | Tumino A.,Columbus Superconductors
Physica C: Superconductivity and its Applications | Year: 2016

In this work, we present a mathematical model which enables to design cylindrical coils with a given central field, made of the superconducting conductor with isotropic Ic(B) characteristic. The model results in a computer code that enables to find out the coil dimensions, and to calculate the coil parameters such as critical current, maximum field in the winding and field non-uniformity on the coil axis. The Ic(B) characteristic of the conductor is represented by the set of data measured in discrete points. This approach allows us to express the Ic(B) as a function linearized in parts. Then, it is possible to involve the central field of the coil, coil dimensions, and parameters of the conductor, including its Ic(B) characteristic, in one equation which can be solved using ordinary numerical non-linear methods. Since the coil dimensions and conductor parameters are mutually linked in one equation with respect to a given coil central field, it is possible to analyze an influence of one parameter on the other one. The model was applied to three commercially available MgB2/Ni/Cu conductors produced by Columbus Superconductors. The results of simulations with the Ic(B) data at 20 K illustrate that there exists a set of winding geometries that generate a required central field, changing from a disc shape to long thin solenoid. Further, we analyze how the thickness of stabilizing copper influences the coil dimensions, overall conductor length, coil critical current, maximum field in the winding. An influence of the safety coefficient in operating current on coil dimensions and other above mentioned parameters is studied as well. Finally, we compare the coil dimensions, overall conductor length as well as coil critical current and maximum field in the winding if the value of required central field changes between 1 and 3 T. © 2016 Elsevier B.V. All rights reserved.

Pitel J.,Slovak Academy of Sciences | Kovac P.,Slovak Academy of Sciences | Tropeano M.,Columbus Superconductors | Grasso G.,Columbus Superconductors
Superconductor Science and Technology | Year: 2015

Abstract The goal of this theoretical study is to illustrate the potential of three different MgB2 tapes, developed by Columbus Superconductors, for application in cylindrical coils. First, the distribution of critical currents and electric fields of individual turns is compared when the winding of the model coil is made with tapes having different Ic(B) and anisotropy values. Second, the influence of the winding geometry on basic parameters of cylindrical coils which consist of a set of pancake coils, such as critical current Icmin, central magnetic field B0 and stored energy E, is analysed. The winding geometry of the coils, i.e. the outer winding radius and the coil length, with the same inner winding radius, was changed from a disc shape to a long thin solenoid in such a way that the overall tape length was held constant, and considered as a parameter. Finally, the winding cross-section of the coil is optimized with respect to the constant tape length in order to reach the maximum central field. The results of calculations show that for a given overall tape length and inner winding radius there exists only one winding geometry which generates the maximum central field. The overall tape length, as a parameter, is changed in a broad range from 500 m to 10 km. All calculations were performed using the experimental data measured at 20 K while the effect of the anisotropy in the Ic(B) characteristic of the short samples is taken into account. © 2015 IOP Publishing Ltd.

Mine S.,General Electric | Xu M.,General Electric | Buresh S.,General Electric | Stautner W.,General Electric | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2013

The authors have reported the results of low n -value from a MgB 2 test coil developed a year ago. A second test coil has been developed with wire of different structure and manufacturing process. Although the n-value related voltage of the second test coil was lower than the first test coil at designed current, it still showed low n-value. A third test coil has been wound with reduced mechanical stress. It also showed very similar n-value related voltage and n-value. Investigation of voltage distribution over the coil indicated that magnetic field was the major factor causing degradation of the n-value and resulting in n -value related voltages. Since the n-value related coil voltages were on the order of 0.1 \mu\hbox{V/cm}, the usual short sample I\rm c test (1 \mu\hbox{V/cm} was the definition of I \rm c ) might not detect the n-value related voltage and might not be able to investigate the cause of low n -value. Therefore, the medium length (\sim10 m) samples were tested and they showed the wire's lengthwise nonuniformity both on n -value and I\rm c, which might be another potential cause of the low n-value of the coil. Along with the electrical investigation, the manufacturing process of the wire was carefully inspected for longitudinal uniformity. Some wire segment samples from the same batch exhibited nonuniformity in the particle size distribution resulting in nonuniform filaments. This might have occurred in the wire for the second and third test coils. © 2002-2011 IEEE.

Nardelli D.,Columbus Superconductors | Matera D.,University of Genoa | Vignolo M.,CNR Institute of Neuroscience | Bovone G.,University of Genoa | And 5 more authors.
Superconductor Science and Technology | Year: 2013

A high-purity MgB4 phase has been synthesized and used as the precursor powder for the realization of in situ wires. Various final heat treatments, from 550 to 1100 ° C for 20 min each, have been carried out to convert the inner mixture to MgB2. Critical current densities up to 1.75 × 106 and 0.98 × 106 A cm-2 at 4.2 and 20 K, with 0.2 T, up to 0.76 × 105 A cm-2 at 4.2 K and 4 T, and up to 0.78 × 105 A cm-2 at 20 K and 2 T were measured. Critical temperatures up to 38.5 K were measured. These results suggest that this could be a good alternative to both ex situ and classical in situ routes. © 2013 IOP Publishing Ltd.

Kulich M.,University of Geneva | Flukiger R.L.,University of Geneva | Senatore C.,University of Geneva | Tropeano M.,Columbus Superconductors | Piccardo R.,Columbus Superconductors
Superconductor Science and Technology | Year: 2013

A substantially different behaviour was observed between MgB2 wires produced either by in situ or ex situ processing after applying the recently developed technique of cold high pressure densification (or CHPD). In contrast to in situ wires, where densification at 1.5 GPa on binary and ternary alloyed in situ MgB2 wires causes an enhancement of mass density and a strong enhancement of Jc, ex situ wires up to 2 GPa show only a negligible enhancement of the MgB2 mass density, while a considerable enhancement of Jc is still observed. In both cases, this reflects an enhancement of grain connectivity, however in ex situ wires, the enhancement of Jc is connected to the partial disruption of the oxide layer around each MgB2 powder particle, in contrast to the enhancement of J c in situ wires, which is correlated to a smaller void fraction and a larger contact area between neighbouring grains. It is well known that J c of ex situ wires decreases after longer exposition times when exposed to air prior to annealing; after several months Jc falls to values ≤50% of the original value. After cold pressing, we have found that Jc of the same wire exceeded the original values, even after exposing the unreacted wire for >1 year to air. A lower electrical resistivity is measured on pressed ex situ MgB2 wires, which confirms the improvement of grain connectivity due to the breakage of the oxide layers. Thus, the application of high pressure at room temperature allows us to recover the values of Jc for ex situ wires even after they have been degraded either by low quality MgB2 precursors or by prolonged ageing of the already formed wire prior to the final heat treatment. The limits of the J c enhancement in ex situ wires are discussed. © 2013 IOP Publishing Ltd.

Morandi A.,University of Bologna | Brisigotti S.,Columbus Superconductors | Grasso G.,Columbus Superconductors | Marabotto R.,ASG Superconductors
IEEE Transactions on Applied Superconductivity | Year: 2013

The feasibility of a conduction-cooled MgB2 -based superconducting fault-current limiter with fast recovery is investigated. A real-scale device for a distribution network is considered. The dc resistive configuration is chosen in order to avoid ac losses and to allow conduction cooling. A high-heat-capacity cable is specifically developed in order to cope with the requirement of fast recovery. A short-length sample of the cable is manufactured in order to assess its feasibility. The detailed design of a prototype is also carried out, and the performance is numerically investigated. © 2002-2011 IEEE.

Pelegrin J.,University of Zaragoza | Romano G.,CNR Institute of Neuroscience | Martinez E.,University of Zaragoza | Angurel L.A.,University of Zaragoza | And 5 more authors.
Superconductor Science and Technology | Year: 2013

In the design and feasibility of electric power applications with MgB 2 conductors, thermal conductivity plays an important role. In composite wires and tapes it is mainly determined by the amount of stabilizer (usually copper), while for coils the electric insulation and epoxy binder characteristics are added. In this paper we present results on quench development and propagation on isolated superconducting tapes and small single pancake coils cooled by thermal conduction, for three types of MgB2 tape with different stabilizations. The quench parameters at different temperatures, such as minimum quench energy (MQE), minimum propagation zone (MPZ) and quench propagation velocity (vp), are reported. A complete electrical and thermal characterization of the superconducting tapes and of non-superconducting materials used in the coil manufacture has been made. With these data, numerical computational models using finite element simulations have been performed for isolated wires and single pancake coils, and the results of the relevant quench parameters have been compared with the measured values. © 2013 IOP Publishing Ltd.

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